CODEWITHSUNDEEP
carraysstruct
Pete Darrow
Pete Darrow

Reputation: 455

Find out the size of a lookup table in C

Is there a way to determine the number of message elements in the following look-up table or do I need to explicitly have an int size in the struct?

typedef struct {
    int enable;
    char* message[3];
} lookuptable;

lookuptable table[] = {
    {1, {"Foo", "Bar", "Baz"}}, // # 3
    {1, {"Foo", "Bar"}},        // # 2
    {1, {"Foo"}},               // # 1
    {1, {"Foo", "Baz"}},        // # 2
};

Upvotes: 0

Views: 428

Answers (2)

Chris Dodd
Chris Dodd

Reputation: 126408

There will always be exactly 3 message elements in the message array, because you have defined it as having a size of 3. Those elements of the array you don't initialize will be initialized to NULL, so you can loop through the initialized (non-null) elements with:

lookuptable *table_entry = ...
for (int i = 0; i < 3 && table_entry->message[i]; i++) {
    ...do something...

It might be a good idea to replace the constant 3 with a #define constant, so it only exists in one place. Or you could use the sizeof(array)/sizeof(array[0]) trick:

for (int i = 0; i < sizoef(table_entry->message)/sizeof(table_entry->message[0]) && table_entry->message[i]; i++)

Upvotes: 1

user1944441
user1944441

Reputation:

No there is no way to do that. You will have to store the number of elements somewhere or terminate the array with a magic number or a NULL.

Upvotes: 3

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